cleanups in preparation of bigger changes

- fix typo drawForSreenshot misspelled
- get rid of DisplayDeviceBase
- removed unused or unneeded code
- always pass a DisplayDevice to Layer methods that are called
  on a per-display basis (to make it clear that this could be
  called more than once per composition).

Change-Id: Id948b7e09fe5c06db0e42d40d6ed75dd095c7f44
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index ca41bd3..872ab98 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -189,6 +189,8 @@
 
     void eventControl(int event, int enabled);
 
+    nsecs_t getRefreshTimestamp() const;
+
     // this class is only used to fake the VSync event on systems that don't
     // have it.
     class VSyncThread : public Thread {
@@ -235,6 +237,10 @@
     size_t                          mVSyncCount;
     sp<VSyncThread>                 mVSyncThread;
     bool                            mDebugForceFakeVSync;
+
+    // protected by mLock
+    mutable Mutex mLock;
+    mutable nsecs_t mLastHwVSync;
 };
 
 // ---------------------------------------------------------------------------